Field of the Invention
The present invention relates to a circuit configuration for producing a load-independent DC voltage, having the following features:
a first rectifier configuration with an AC voltage terminal and two output terminals; PA1 a current control configuration for controlling the mains current consumption, which is connected to the output terminals of the first rectifier configuration and has two output terminals; PA1 a second rectifier configuration connected to the output terminals of the current control configuration and having output terminals at which an output voltage can be tapped; PA1 a voltage measurement configuration furnishing a voltage signal at an output, which is connected to the output terminals of the second rectifier configuration; PA1 a feedback branch with a control configuration with an integrator configuration for feeding the voltage signal back to an input terminal of the current control configuration. PA1 a first rectifier configuration having an AC voltage terminal and two output terminals; PA1 a current control configuration for controlling the mains current consumption, the current control configuration being connected to the output terminals of the first rectifier configuration, having two output terminals, and an input terminal; PA1 a second rectifier configuration connected to the output terminals of the current control configuration and having output terminals furnishing an output voltage; PA1 a voltage measurement configuration connected to the output terminals of the second rectifier configuration, the voltage measurement configuration providing a voltage signal; PA1 a feedback branch connected to receive the voltage signal from the voltage measurement configuration and to feed the voltage signal back to the input terminal of the current control configuration, the feedback branch including a control configuration with an integrator; PA1 a function generator connected downstream of the control configuration in the feedback branch, the function generator producing an output signal which depends on an input signal according to a function f(x), wherein a derivative of the function f(x) is dependent on an input signal, and the derivative rises at least partly with an increasing input signal.
The object of circuit configurations of this type, which in particular are used in switched mode power supplies, is to provide as output voltage a DC voltage for the consumers which can be connected to the output terminals, the output voltage maintaining its value for load variations within a predetermined range.
If the mains voltage remains the same, a load variation occurring at the output terminals requires a variation in the, in particular sinusoidal, current consumption controlled by the current control configuration. If the current consumption and therefore the power consumption initially remain the same as the load varies, then a variation in the output voltage takes place. This variation is registered by the voltage measurement configuration and fed back as a voltage signal via the feedback branch to the current control configuration, so as to correct the current consumption in accordance with the load variation, until the output voltage again reaches the specified value. In order to avoid feedback of unavoidable variations in the output voltage around the specified value, which occur in particular when simple second rectifier configurations are used, integration of the control signal in the control configuration of the feedback branch is conventionally provided in circuit configurations of this type. Owing to a normally large integration time constant, load variations and therefore variations in the output voltage are fed back to the current control configuration with a delay, and the correction of the current variation therefore is relatively sluggish.
The variation in the current consumption is also necessary in the event of a variation in the mains voltage. This is particularly relevant when the circuit configuration is used in "extended-range" power supplies which are intended to deliver an output voltage which remains the same for input voltages between about 90V and 265V. If the input voltage varies, then the mains current consumption firstly varies proportionately to the voltage variation, while the power taken in and given out by the circuit configuration depends on the square of the voltage variation. If the current consumption is at first not corrected, then the output voltage firstly falls, for example when the mains voltage is reduced, this variation being registered by the voltage measurement configuration and fed back as in integrated voltage signal via the feedback branch to the current measurement configuration.
Both in the event of a load variation and in the event of a variation in the mains voltage, the current consumption is corrected until the output voltage is again set to the specified value.
The controlling of the current consumption in the current control configuration takes place with the use of a control loop which is fed with a weighted mains voltage signal, the current consumption being set proportionately to this signal. Conventionally, the generation of the weighted mains voltage signal takes place by multiplying a control signal applied to the input terminal of the current control configuration by a mains voltage signal depending directly on the mains voltage.
If, for example for the same load, the output voltage applied to the output terminals and therefore the power put out is to be maintained when the mains voltage is halved, then it is necessary to double the original current consumption, that is to say the mains voltage signal is to be weighted with a factor of four in order to achieve a current consumption which is twice as large as the original current consumption. The control signal applied to the input terminal of the current control configuration is therefore dependent on the square of the mains voltage, the signal being commensurately larger as the mains voltage is smaller.
Equal load variations at the output terminals of the current control configuration cause equal voltage variations in the output signal, while a signal variation which depends on the mains voltage is required at the input terminal. A variation in the signal applied to the input terminal must take place proportionately to the load variation, that is to say the control signal must halve if, for example, the load is halved. Since the signal excursion of the voltage signal is merely load-dependent, but the signal excursion of the control signal applied to the input terminal of the current control configuration is dependent on the mains voltage, correction of the output voltage for equal load variation at the output takes a different length of time for differing mains voltages. The time taken for the equalization thus increases nine-fold when the input voltage is reduced by a third for equal load variation.
To avoid this problem in the prior art circuit configuration of this type, the root mean square of the mains voltage is taken in account when forming the weighted mains voltage signal. The averaging is effected with a multipole low pass filter, which is very expensive.
In another prior art circuit configuration, a changeover switch is provided which carries out additional weighting of the mains voltage signal in a ratio of 1:4. That weighting is exact only for two different input voltages, usually 120 V and 240 V.